What is HEV (high-energy visible) light?
By Spektrum Glasses Editorial Team · Published 2026-08-06 · Updated 2026-08-06 · Facts re-checked 2026-08-06 How this page is written and checked: our editorial method · how we verify claimsShort answer
HEV (high-energy visible) light is the shortest-wavelength part of the visible spectrum, roughly 380-500 nm, seen as violet through blue-cyan and sitting immediately above ultraviolet. Its photons carry more energy than the rest of visible light, and the 460-480 nm region is where the human circadian system is most sensitive.- HEV spans roughly 380-500 nm, the violet-blue end of visible light, just above UVA.
- Photon energy is inversely proportional to wavelength: 400 nm is about 3.1 eV, 700 nm about 1.8 eV.
- The band is not uniform: hazard weighting peaks in the mid-400s, circadian sensitivity peaks at 460-480 nm.
- Daylight is by far the largest HEV source; screens are a much smaller contributor.
- A filtering percentage means nothing without the wavelength or band it was measured over.
Where HEV sits in the spectrum
Visible light runs from about 380 nm to about 700 nm. HEV is simply the short-wavelength end of that range, conventionally taken as 380-500 nm, which the eye perceives as violet, blue and blue-cyan. Below 380 nm you are into UVA (roughly 315-400 nm), which is invisible. Above 500 nm you are into green, yellow and red. The “high energy” part is a straightforward consequence of physics, not a warning label. Photon energy is inversely proportional to wavelength: E = hc/lambda, which works out to approximately 1240/lambda(nm) electronvolts. So a 400 nm photon carries about 3.1 eV, a 500 nm photon about 2.5 eV, and a 700 nm red photon about 1.8 eV. HEV photons carry roughly 75 percent more energy than deep red photons. That is the whole of what the term means.
Note that 400 nm is a boundary of convention, not of physics. Nothing changes about a photon at 399 nm versus 401 nm except that one is called ultraviolet and the other is called visible.
The band is not one thing
Treating 380-500 nm as a single quantity is the most common error in how blue light gets discussed. Two sub-regions inside it behave quite differently and are studied for different reasons. The first is the photochemical hazard region, in the low-to-mid 400s. When laboratories calculate a “blue-light hazard” figure they apply a weighting function that peaks in the mid-400 nm range and falls away steeply on either side, so energy at 435 nm counts for far more than the same energy at 480 nm. The second is the circadian region, 460-480 nm. This is close to the peak sensitivity of melanopsin, the photopigment in a small population of intrinsically photosensitive retinal ganglion cells that signal ambient light level to the brain’s master clock. These cells are not part of image formation; they are a light meter. A lens can be strong in one region and weak in the other. Our own COLTS-measured clear lens illustrates this well, because the transmittance curve is steep rather than flat:- 400 nm: 99.99 percent filtered
- 410 nm: 95.1 percent filtered
- 420 nm: 63.0 percent filtered
- 450 nm: 33.1 percent filtered
Where HEV actually comes from
The dominant source of HEV exposure for almost everyone is the sun. Daylight is broad-spectrum and outdoor illuminance is enormously higher than anything a display produces at the eye. The exact ratio depends on time of day, cloud cover, screen brightness and viewing distance, but the direction is not in dispute: a person who spends time outdoors receives far more HEV from the sky than from a monitor. Screens and modern lighting do have a distinctive spectral signature, though. Most white LEDs are built from a blue emitter, typically near 450 nm, coated with a phosphor that converts part of that blue into a broad yellow band. Mixed together, they look white. That construction leaves a visible spike near 450 nm in the emission spectrum of LED bulbs, LED-backlit displays and phone screens. So screen light is not unusually intense in absolute terms, but its blue content is concentrated at a particular wavelength rather than spread evenly. This matters for evaluating any filtering claim. A lens designed around the near-UV edge at 400-410 nm will do very little to the 450 nm LED spike. A lens designed around the 450-480 nm region has to remove enough blue to be visibly tinted.What a lens can and cannot do about it
Blue is a color you can see. Removing it changes what the world looks like, and there is no way around that trade-off. A lens that is genuinely near-clear can only take a slice of the band; a lens that takes the whole band is visibly amber, orange or red. Our measured numbers show both ends of this. The PROSPEK clear lens has 91.6 percent visible (photopic) transmission, which is close to no tint at all, and its filtering is concentrated at the short end as listed above. Our ZENOX clear lens averages about 52 percent across the blue band with 100 percent UV filtering. The amber evening lens, by contrast, filters 97.9 percent across 400-500 nm and 98.3 percent at the 460-480 nm circadian band, but it is obviously orange to look through. The orange lens measures 99.96 percent across 380-500 nm and the red 99.83 percent. Neither the orange nor the red lens is suitable for driving, because filtering that deep distorts color recognition, including signal and brake lights. On effectiveness, the published evidence is modest. Leung, Li and Kee (PLOS ONE, 2017) measured commercially available blue-light-filtering lenses and found they reduced the calculated blue-light hazard by roughly 10 to 24 percent. That is a real optical effect and a small one. Whether a given person notices any subjective difference from a spectral change of that size is a separate question, and the evidence for symptom benefit is limited and contested. We publish transmittance data because that is what can be measured; we do not make medical claims, and PROSPEK eyewear is non-prescription.How to read a blue-light filtering number
If you want to compare lenses honestly, five questions do almost all the work.- Over what wavelength or band? A single-wavelength figure at 400 nm is easy. An average across 400-500 nm is hard. If the band is missing, the number is not a claim you can check.
- Peak or average? “Up to 99 percent” usually means the best single point on the curve. Ask for the average.
- Who measured it? Testing done by an accredited laboratory means the lab’s competence has been assessed against ISO/IEC 17025 by an accreditor such as A2LA. In-house marketing measurements are not equivalent.
- By what method? Spectral transmittance for non-prescription eyewear is measured under ANSI Z80.3. Naming the method lets someone reproduce the result.
- What is the visible transmission? Without it you cannot tell whether a high blue-filtering figure comes from clever coating design or simply from a dark tint. A lens at 91.6 percent photopic transmission and a lens at 30 percent are different products even if they quote the same blue number.